1. Field of the Invention
The present invention relates to a magnet that contains decreased amounts of heavy rare earth metals and exhibits high energy product or high heat resistance, to a method for producing the same, and to a rotating machine equipped with such a magnet.
2. Description of Related Art
A conventional rare earth sintered magnet containing a fluoride compound or an oxyfluoride compound is disclosed in Patent Literature 1. In the conventional technology, the fluoride compound used for processing is a mixture of a powdery compound or powder of the compound and a solvent, and it is difficult to efficiently form a phase containing fluorine along surfaces of magnetic particles. In the above-mentioned conventional method, the fluoride compound used for the processing is in point contact with the surface of the magnetic particles, and it is difficult for the phase containing fluorine to come in surface contact with the magnetic particles. Therefore, there are required a large amount of the processing material and heat treatment at high temperatures.
On the other hand, Patent Literature 2 discloses a mixture of micro-structured powder of rare earth fluoride compound (1 to 20 μm) and NdFeB powder. However, there is disclosed no example of growth of the micro-structured powder of rare earth fluoride compound in the grain of the magnet in a state of discrete plates.
Non-Patent Literature 3 discloses a magnet that includes a micro sintered magnet coated on the surface thereof with micro particles (1 to 5 μm) of DyF3 or TbF3. Although it is described in the above-mentioned literature to the effect that the fluoride compound is applied by a treatment other than the treatment with a solution of the fluoride compound and that Dy and F are absorbed by the sintered magnet to form NdOF and Nd oxide, there is in the Non-Patent Literature 1 no teaching on the relationship between concentration gradients of carbon, heavy rare earth metals, light rare earth metals in the oxyfluoride compound and direction of anisotropy.
[Patent Literature 1] JP, 2003-282312, A                [Patent Literature 2] U.S. patent US2005/0081959A1        [Non-Patent Literature 1] Page 3846 from IEEE TRANSACTIONS ON MAGNETICS and VOL. 41 No. 10 (2005) Page 3844        